short



Dec. 21, 1948.

Filed July 23, 1945 B. SHORT HIGH-FREQUENCY IGNITION SYSTEM 3Shets-Sheet 1 fnyine driven shaft drzlz/ej ihe igm'lz'on timer can andMe variable condenser r0101:

INVENTOR J6 BY I Filed July 23, 1945 3 Sheets-Sheet M w n m 0 n" EYYY Q7 INVENTOR firaaks H 51502-2 ATTOR EY/I Patented Dec. 21, 1948HIGH-FREQUENCY IGNITION SYSTEM Brooks H. Short, Anderson, Ind., assignorto General Motors Corporation, Detroit, Mich., a corporation ofDelawarev Application July 23, 1945, Serial No. 606,645

19 Claims.

This invention relates to a high frequency ignition system for aninternal combustion engine.

This application is a continuation in part of my application, Serial No.530,288, filed April 10, 1944.

The object of the present invention is to provide ignition even thoughthe engine may be operating under high compression and the spark plugsmay be fouled. In the disclosed embodiments of this invention, thisobject is accomplished by providing at each spark plug, a resonator, theresonators of the different spark plugs being tuned to differentfrequencies, an oscillator having a variable condenser which can beadjusted to tune the oscillator successively with the various resonatorsat the spark plugs, a timer for controlling the operation of theoscillator and mechanically connected with its variable condenserwhereby ignition is provided at the engine spark plugs in recurrentsequence.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings, wherein preferred embodiments of the present invention areclearly shown.

In the drawings:

Fig. 1 is a wiring diagram of one embodiment of the present invention inwhich the operation of the oscillator is effected by'the voltageobtained from an induction coil.

Fig. 2 is a wiring diagram of a modified form in which operation of theoscillator is efi'ected by voltage obtained from a power pack.

Fig. 3 is a longtitudinal', sectional View of the ignition timer and thevariable condenser of the oscillator.

Fig. 4 is a sectional View on line 4-4 of. Fig- 3.

Fig. 5 is an enlarged fragmentary, sectional View on enlarged scale online 5-5 of Fig. 4.

Fig, 6 a longitudinal, sectional View of'a part of one of the resonatorsassociated with a spark plug.

Referring to Fig. 1, 28 designates a battery, preferably 24 volts, oneterminal of which is grounded at 2!. The other terminal of. the batteryis connected through a switch 22 with one terminal of a primary winding23 of an induc coil 24 having a secondary winding 25 connected to theother primary terminal which is connected also to a fixed contact26-insulatingly supported on a stationary plate 21 of a timer T. Thecontact 26 cooperates with. a movable contact 28 carried by a lever2811' connected by spring blade 280 with ground. Spring blade 28c urgesthe rubber block 281) mounted on. lever 28a toward a timer cam 29 drivenbyshaft sindicated 40 The operation of the system is as follows:

- 2 by the vertical dot-dash line. The contacts 26 and 28are shunted bya condenser 26a which reduces sparking at the contacts.

The induction coil secondary 25 is connected with a cold cathode diode30, a high frequency choke 3|, wire 32 and. plate 33 of a thermionictube 34; The tube 34 is also provided with a cathode 35 and a grid. 36.The cathode 35 is. connected at one end by a lead 31 which is in turnconnected with the battery 20 through a switch 38. Thus, when the switch38 is closed, the cathode will be heated. A condenser 40 is connectedacross the cathode leads 3'! and 39. The grid 36 is connected by a wire4| to a grid resistance 42 and a condenser 43 which are connected bywire 46 to one end of a primary of an oscillator coil 44. Primary 45 hassections 45a and 45b connected with ground tap 450. The other end ofprimary 45 is connected by a wire 41 with a condenser 48 which isconnected with wire 32. An adjustable core 43 extends within the primarycoil 45.

Associated with the primary is a secondary winding 58' of a few turns inwhich is induced a high frequency current of low voltage and highamperage. The secondary 58 is connected in series with primary coils 5|,52, 53 and of resonators 55, 56, 51 and 58 respectively, havingsecondary windings 6|, 62, 63 and 64 respectively, connected with thespark gaps of spark plugs 65, 66, 61 and 68 respectively, and each witha condenser '10. The natural frequencies of the resonators aresubstantially different and are determined by iron rods H which can beso adjusted as to project different distances within the secondarywindings of the resonators.

The frequency of the oscillatory current in coil 44 is determined by avariable condenser 15 connected to wires 46 and 41.

When the switches 22 and 38 are closed a primary circuit is completedincluding the storage battery 20, ignition switch 22, the contacts 26,28 of the engine driven ignition timer and the primary of the inductioncoil 24 designed to give the required secondary voltage when thecontacts 26, 28 of the ignition timer separate through the cold cathodediode 33 which prevents discharge of the secondary until a secondaryvoltage has been reached 4 which is effective so to operate the circuitthat ignition will be provided by a fouled spark plug. This avoidsdraining off energy due to leakage at the plug: when the secondaryvoltage is rising. When this voltage is applied to the plate 33 of thethermlonic'tube 34, the tube becomes conducting and, as will beexplained in detail later. high frequency oscillations are produced inthe oscillator primary coil 45. In the secondary 50 of relatively fewturns, there is induced a high frequency; current of low voltage andhigh ampei age.

The frequency of the oscillator is determined by the adjustment of themovable plates of the condenser which are connected in a manner to bedescribed with the ignition timer cam 29. When the time arrives for thefiring of a certain engine cylinder, the timer contacts separate; and,at that instant, the movable plates of the variable condenser 15 are sopositioned that the oscillator 44 is tuned only to the resonatorassociated with that spark plug which is in the cylinder to be fired.For that reason, a spark of high voltage and frequency will occur onlyat the gap of that spark plug. Sparking does not occur at the other gapsof the resonators not in tune with the oscillator at the time of discharge of coil 24 because the resonator which is in tune with theoscillator receives a very large portion of the total wattage. Hence theresonators of the spark plugs not to be fired receive a voltage too lowto jump the spark gap.

The circuit shown in Fig. 2 does not use a timer controlled inductioncoil for impressing a voltage on the oscillator but uses instead a highvoltage source whose voltage is impressed upon the oscillator by a timercontrolled thyratron. As shown in Fig. 2, the high voltage source is apower pack or vibrator power supply I00, having high voltage outputterminals I03 and H34 having low voltage input terminals IOI and I02connectible by switch 22 with a relatively low voltage storage batteryAs will be understood by those skilled in the art, the power pack I00provides means for transforming low voltage direct current to highvoltage direct current which, for example, may be four thousand voltsacross the terminals I03 and I04. These terminals are connected withvoltage divider resistances I05 and I06 connected with a tap I01. Thetotal resistance of elements I05 and I06 is, for example, 150,000 ohmsand the voltage between the tap I01 and terminal I03 is two hundredvolts. The tap I01 is connected through a resistance I08, preferably2500 ohms, with the breaker lever 23a of timer T.

A hydrogen filled thyraton tube IIO provides a plate III, a grid II2, acathode H3 and a cathode heater filament II4. Plate III is connectedwith the cathode of tube 34 by wire H5 and wire 31 which is connectedwith the battery switch 22 and with the power pack terminal IOI. Thegrid I I2 is connectedby wire IIS with timer contact 26. Cathode H3 isconnected by wire II1 with resistance I05 and with power pack terminalI03. Filament H4 is connected by wire II8 with wire 31 and with aresistance II9 of a value suitable for use with the thyratron IIO. WireI20 connects radio frequency choke 3| with resistance I06 and with powerpack terminal I04. A resistance I2l, preferably 5000 ohms, connectswires H6 and H1.

The operation of the system shown in Fig. 2 is as follows: While contact28 is separated from contact :35, the thyratron H0 does not pass currentand the oscillator is inactive. When contact 28 engages contact 26 thefollowing circuit of the grid I I2 is established: Voltage divider I01,resistance I00, contacts 28 and 26, wire II6, grid II2, cathode II3,wire II1. Therefore nearly 200 volts is impressed on the grid II2. Thiscauses the thyratron IIO to become conductive and to impress upon theplate 33 of tube 34 the voltage across the power pack terminals I04, I03through the following circuit: Terminal I04, wire I20, choke 3|, wire32, plate 33 of tube 34, cathode 35, wire 31, wire H5, plate III ofthyratron IIO, cathode H3, wire Ill, power pack terminal I03. Thiscauses the oscillator to become operative whereby oscillations occur inthe oscillator coil primary 45 of a frequency depending upon theadjustment of the variable condenser 15 which is controlled in timedrelation with the timer cam 29; and ignition will be provided at thatspark plug associated with the resonator with which the oscillator is intune at the instant of engagement of contacts 28 and 2'6.

The operation of the oscillator is the same in both circuits. In Fig. 1,the oscillator begins to operate when, due to the discharge of energy ofthe ignition coil 24 following separation of the timer contacts, thecold cathode diode 30 becomes conducting. The oscillator operating inFig, 1 when the coil is discharged. In Fig. 2, the closing of thecontacts causes the oscillator to operate and the opening of thecontacts causes it to cease operating. Whenever a sufficient voltage isimpressed on the plate 33 of tube 34 either by opening the contacts inFig. l or closing the contacts in Fig. 2, the oscillator tube 34 permitscurrent to flow to charge the condenser 15. In Fig. 2, the condensercharging circuit includes power pack terminal I04, wire I20, choke 3|,condenser 40, condenser 15, resistance 42, wire 4I, grid 36, cathode 35,wire 31, wire II5, plate III, cathode II3, wire H1 and power packterminal I03. During the charge of condenser 15, the voltage impressedon the grid 36 becomes increasingly positive. As grid 36 becomes moreositive, tube 34 passes more current and the Vol aire drop across thetube decreases. As the Voltaire drop decreases across tube 34, the co.,er 15 starts discharging and produces a negat ve volt-- age on the grid36 due to the operation of tr cluctively related circuits. One of thesecondenser 15, wire 41, all of the oscill coil 45 and Wire 45; the othercircuit .mcludes the grounded tap 450 of primary 45, the primary section45a, wire 46, resistance 42, wire 4|, grid 36, cathode 35 and groundconnection back to 45c. The negative voltage impressed on grid 36 causesless current to flow from the plate 33, thereby raising the voltage dropacross the tube 34 and allowing the condenser 15 to be charged again. Inthis way, an oscillation through the primary 45 is sustained. Thisoscillation increases rapidly in amplitude until the maximum amplitudeis reached; and the oscillation is sustained so long as sufficientvoltage is impressed on the plate 33 of oscillator tube 34. In otherwords, the oscillator tube 30 operates in a manner analogous to avariable resistance in shunt with the condenser 15. As condenser chargeincreases the variable resistance decreases automatically; and, when thedecrease of resistance is such that the condenser is robbed of chargingcurrent, the condenser discharges. The discharge of the condenserautomatically causes the variable resistance to increase whereby thecondenser is pen mitted to receive a charging current; and the cycle isrepeated so long as sufficient voltage is being impressed on the plate33 of tube 34.

As the current oscillation through the oscillator primary coil 45increases in magnitude that resonator with which the condenser 15 istuned will have, in its condenser-coil circuit, correspondingoscillation increasing in magnitude until voltage impressed upon thespark plug is with cient to cause the current-to jump the gap. Asstatedbefore; only the resonator which is in tune with the oscillator receivesthe benefit of the alternating charge and discharge of the condenser 15.

The ignition unit which comprises the ignition timer: and the variablecondenser will now be described, with reference to Figs. 3, 4 and 5. Atimer housing I30 supports circuit breaker plate 21 which pivotallysupports the breaker lever 28a having the rubbing block 28b urged byspring 280 toward the camlfl driven in any suitable manner by the enginethrough the shaft S. If the timer has both contacts insulated as shownin Fig. 2, terminal 28d, insulatingly supported by the housing, would beconnected with the resistance I08 and with spring 280'. Another terminal(not shown), insulatingly supported by the housing, would be connectedwith contact 26 and wire I I6. According to thecircuit shown in Fig. l,the terminal which is insulatingly supported by the housing and isconnected with contact 26 would be connected with primary coil 23 andwith the condenser 26a which, as shown in Fig. 3, is secured by a clip26b and a screw 26c to the breaker plate l1 upon which the condenser 20ais grounded.

To the timer housing I30 there is secured a condenser housing I3'Ihaving a wall I32 which separates the timer from the condenser 15 inchamber I33 which is closed by a cover I34 sealed by a gasket I35. CoverI34 is secured to housing I3I by screws I36. The condenser 15 comprisesfour stationary plates I40 and five movable plates I4I. Two of thescrews I36 pass through the plates I40 and metal spacer sleeves I42 andmetal washers I43. The stationary plates I 40 are electrically connectedwith each other by the spacers and screws and are connected by a strapI44 with a terminal I45.

The movable plates I4I are each provided with an aperture I46 having aflat I41 which engages a similar flat provided by a non-metallic rod I48which extends through the opening I46 in the plates I4I. Rod I48 has anenlarged portion I49 which provides a shoulder I50 against which theplates and intermediate metal spacers I 5i are urged by the hex-portionI52 of a screw I53 threaded into a tapped opening in the rod I48. ScrewI53 has an extension I54 journaled in a bearing I55 supported by thecover I34. A carbon brush I56 bears against the upper end of the partI54 and receives a spring blade I51 connected with a terminal I58attached to the cover I 34. The rod I48 has an extension I59 passingthrough a metal sleeve I and attached thereto by a cross pin ISI. Thesleeve I60 is journaled in a bearing I62 provided by wall I32 of housingI3I and is supported vertically thereby, said bearing being engaged atits upper end by a washer I63 which is sprung into a groove I64 providedby the sleeve I60. Sleeve I60 provides a tang I which enters a notch I66provided by cam 29 thereby drivingly connecting the cam 29 with thecondenser plates MI in a predetermined relation.

The condenser plates I40 and MI are coated with a material (I4Ia in Fig.5) having high specific inductive capacity. A suitable polymer of thischaracter, such as polystyrene is dissolved in butyl acetate to make asolution about the consistency of new maple syrup. To this is added anominal amount of silicon resin. The condenser plates are coated bydipping. The plates I40 may be dipped separately or while beingmaintained in assembly with the spacers I42 by.

means of short screws and nuts (not shown) in lieu of the screws I36.dipped separately but can be dipped when assembled with the spacers l5I,rod I48 and screw I53. Each coat is very thin for example, .00025 thick.After'dipping, the coated plates are placed for ten minutes in a vacuumchamber at 5" to x 7" Hg vacuum. Then the coat is thoroughly Thisprocess is repeated as many dried in air. times as necessary to obtainthe desired total thickness of .050" to .060", for example. The

result is a coating having satisfactory dielectric strength and specificinductive capacity. The condenser plates are made of aluminum and withrounded edges; and they are flattened and polished to a mirror finishbefore coating.

Fig. 6 shows a unit which includes an assemby of parts of eachresonator. The unit comprises a non-conducting body I10 upon which iswound the resonator secondary such as secondary 6| connected at one endwith a terminal l and at the other end with a conductor I12 connectedwith a threaded bushing I13 adapted to be screwed on the insulatedterminal of a spark plug. Since the spark plug is grounded on theengine, the terminal screw I1I would be connected with ground throughthe engine. frame or cylinder block. The resonator condenser 10 would beconnected between the screw The non-conducting Ill and the bushing I13.

body I10 is provided with a central bore I14 for receiving the tuningrod 1I shown in Fig. 1. The rod is adjusted relative to the coil 6| byturning a screw I15 attached to the rod TI and threaded through abushing I16 screwed into the body I10, the rod I1I being retained in theadjusted position by tightening a lock nut I11. The resonator primarycoil, such as coil 5I, is merely dropped over the body I10 and locatedaround the secondary coil 6|. The oscillator secondary 50 and theseveral resonator primaries H, 52, 53 and 54 may be formed of onecontinuous piece of wire. The spark plug has the ca-" bustion enginehaving a', spark-plug; a time!" operated by the engine; an oscillatorincluding a coil and a condenser; a resonator connected with the sparkplug and inductively coupled with the oscillator coil; an oscillatorcontrol tube respimsive to the application of a required voltage forcausing operation of the oscillator; and means under control by thetimer for effecting the application of the required voltage upon thecontrol tube at the time when ignition is required.

2. An ignition system according to claim 1 in which the control tube isrendered conducting by the application of a required plate voltagewhereby the condenser can be charged through its grid-to-cathodecircuit, said tube operating-'- in response to increase of condensercharge to" increase voltage drop between its plate and V cathodewhereupon the condenser discharges through the oscillator coil, acircuit including the" tube grid and a portion of the oscillator 'coil"whereby discharge of the condenser through 'the The plates I II may beof the present invenis to be understood that other forms might beadopted, all coming within the scope oscillator coil causes the voltagedrop between the plate and cathode to decrease whereupon the charging ofthe condenser is resumed.

3. An ignition system according to claim 1 in which the means under thecontrol of the timer is an induction coil having a, primary windingconnected by the timer intermittently with a current source and having asecondary winding connected with the device, a voltage being generatedin the secondary winding when the timer operates to disconnect theprimary winding from the current source.

4. An ignition system [or a multi-cylinder internal combustion enginehaving a spark plug in each cylinder, a plurality of resonators havingdifferent frequencies and connected respectively with the spark plugs.an oscillator, means for inductively coupling the oscillator with theresonators, an oscillator control tube responsive to the application ofa required voltage for causing the oscillator to operate, a timeroperated by the engine, means under control by the timer for causing theapplication of the required voltage upon the control tube at the timewhen ignition is required, and means operated by the engine foradjusting the oscillator for operation, successively in recurrentsequence, at frequencies corresponding to the frequencies of theresonators.

5. An ignition system for multi cylinder internal combustion enginehaving a spark plug in each cylinder, a plurality of resonators havingdifferent frequencies and connected respectively with the spark plugs,and each including an induction coil having a secondary windingconnected with a spark plug and having a primary winding, an oscillatorincluding an induction coil having a. secondary winding connected withthe resonator primary windings in series and including a control tuberesponsive to the application of a required voltage for causing theoscillator to operate, a timer operated by the engine, means undercontrol by the timer for causing the application of the required voltageupon the control tube at the time when ignition is required, and meansoperated by the engine for adjusting the oscillator for operation,successively, in recurrent sequence, at frequencies corresponding to thefrequencies of the resonators.

6. An ignition system for a multi-cylinder internal combustion enginehaving a spark plug in each cylinder, a plurality of resonators havingdiil'erent frequencies and connected respectively with the spark plugs,an oscillator, means for inductively coupling the oscillator with theresonators, an oscillator control tube responsive to the application ofa required voltage for causing the oscillator to operate, a timeroperated by the engine, means under control by the timer for causing theapplication of the required voltage upon the control tube at the timewhen ignition is required, means operated by the engine for adjustingthe oscillator for operation successively in recurrent sequence atdifferent frequencies, and means provided by each resonator foradjusting its frequency to that which the oscillator has at the timewhen ignition is required at the plug connected with that resonator.

'7. An ignition system for a multi-cylinder internal combustion enginehaving a spark plug in each cylinder, a plurality of resonators havindifferent frequencies and connected respectively with the spark plugs,an oscillator including a coil and a variable condenser having movableplates by which the oscillator can be adjusted for operation,successively in recurrent sequence,

at frequencies corresponding to the frequencies of the resonators, meansfor inductively coupling the oscillator coil with the resonators, anoscillator controller responsive to the application of a requiredvoltage for causing the oscillator to operate, a timer operated by theengine, means under control by the timer for causing the application olthe required voltage upon the control tube at the time when ignition isrequired, and means operated by the engine in synchronism with the timerfor moving the movable plates of the variable condenser.

S. An. ignition system for an internal combustion engine comprising, aresonator including an induction coil having a primary winding and asecondary winding, the secondary winding being connected with a sparkplug; an 0*: tune with the resonator and including a control tube, acondenser and an induction coil having a primary winding connected withthe tube and the condenser and having a secondary winding connected.With the primary winding of the resonator; an engine operated timer; andmeans under control by the timer for impressing such voltage upon theplate of the oscillator tube that the oscillator becomes operative.

9. An ignition system according to claim 3 in which the means undercontrol by the timer includes an induction coil having a secondarywinding connected with the oscillator tube plate and having a primarywinding connected by the timer with a current source.

10. An ignition system according to claim 8 in which the means undercontrol by th includes a thyratron for connecting the etc .ator tubeplate with a current source, and in which the grid circuit of thethyratron is under control by the timer.

11. An ignition system for an internal ccmbusticn engine comprising, aplurality of resonators having different frequencies each including aninduction coil having a primary winding and a secondary Winding, saidsecondary winclliz be ing connected respectively with spark plu anoscillator including a control tube; a variable condenser having arotatable element and in cluding an induction coil having a primarywinding connected with the tube and the con ilcnser and having asecondary Winding connected in a series circuit including the primarywindings of the resonator induction coils; a timer; meme-s driven by theengine for operating the timer and the rotatable element of the variablecondenser in order to tune the oscillator sequentially with theresonators at the times when ignition is re quired; and means undercontrol by the timer for impressing such voltage upon the plate of theoscillator tube that the oscillator becomes opera tive.

12. An ignition system according to claim ll in which the means undercontrol by the timer includes an induction coil having a secondarywinding connected with the oscillator tube plate and having a primarywinding connected by the timer with a current source.

L3. An ignition system according to claim 11 in which the means underthe control by the timer includes a thyratron for connectin theoscillator tube plate with a current source, and in which the gridcircuit of the thyratrou is under the control of the timer.

14. A timer and variable condenser unit for use in an ignition systemhaving a timcr-con-- trolled oscillator including a variable condenserby which the oscillator is tuned sequentially to a plurality ofresonators inductively associated with the oscillator and respectivelyconnected with spark-plugs, said unit comprising a housing; a circuitmake-and-break device in the housing; a variable condenser supported bythe housing and having a rotatable element; an engine driven membersupported by the housing and operating said device; and means connectingsaid member with the element.

15. A timer and variable condenser unit for use in an ignition systemhaving a timer-controlled oscillator including a variable condenser bywhich the oscillator is tuned sequentially to a plurality of resonatorsinductively associated with the oscillator and respectively connectedwith spark plugs, said unit comprising a housing; a circuitmake-and-break device in the housing; a hollow body supported by thehousing; a variable condenser supported within the housing, saidcondenser having a plurality of spaced apart stationary plates carriedby the body and a plurality of rotatable elements disposed in said bodyin superposed relation and connected in spaced apart relation to oneanother on a shaft journalled in the body; an engine driven membersupported by the housing and operating the device; and means forconnecting the member with the shaft.

16. A resonator unit for use in an ignition system having an oscillatorwhich includes an induction coil having primary and secondary windingsand which includes a resonator induction coil primary winding connectedin series with the secondary winding of the oscillator induction coil,said unit comprising a non-conducting body; a metal terminal supportedthereby and providing for attachment of the unit to a spark plug and theelectrical connection of the terminal with the insulated electrode ofthe spark-plug, a grounding terminal carried by the body, a resonatorsecondary coil surrounding the body and connected with said terminal andthe grounding terminal, a magnetizable core supported by the body andsurrounded by the secondary; and means for adjusting the core relativeto the secondary, said body of the unit providing a support for theresonator primary coil.

17. An ignition system for an internal combustion engine having aplurality of spark plugs, said system comprising a plurality ofresonators connected respectively with the spark plugs and eachincluding a transformer having a primary coil and a secondary coilconnected with the spark plug electrodes and including a condenserconnected with the secondary coil and including an adjustabletransformer core, the location of which determines the frequency of theresonator, the resonators being tuned to different frequencies byadjustment of their cores; an oscillator having a. transformercomprising a secondary coil connected in series with all of theresonator primary coils in series, and comprising a primary coil, andhaving a variable condenser including fixed plates and rotary platesconnected with the end terminals of the oscillator primary coil, andhaving a control tube including a plate connected with one terminal ofthe variable condenser, a grid connected with the other terminal of thevariable condenser and including a cathode connected with the oscillatorprimary coil intermediate its end terminal; a timer including a camdriven by the engine and a pair of engageable contacts one of which isperiodically moved from the other by operation of the cam, an enginedriven member which rotates the rotary plates of the variable condenserin tuned relation to control of the movable contact by the cam; andapparatus under control of the timer contacts for periodically causingimpression upon the plate of the oscillator tube and upon the variablecondenser of a voltage required for oscillator operation.

18. An ignition system according to claim 17 in which the apparatuscomprises a relatively low voltage current source, an induction coilhaving a primary winding connectible through the timer contacts with thecurrent source and having a secondary winding, and cold cathode diodetube connecting the secondary winding with the plate of the oscillatorcontrol tube, a relatively high voltage being induced in the secondarywinding when the timer contacts separate.

19. An ignition system according to claim 17 in which the apparatuscomprises a relatively high voltage current source, a thyratron forconnecting the current source with the plate of the oscillator tube whenthe thyratron becomes conducting, a voltage divider connected with thecurrent source, and a circuit including the thyratron grid, the timercontacts and a portion of the voltage divider, whereby closing of thetimer contacts renders the thyratron conducting.

BROOKS H, SHORT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,347,286 Sandretto Apr. 25, 19442,389,637 Ruben Nov. 27, 1945 2,409,202 Francis Oct. 15, 1946

